JEOS:RP - Journal of the European Optical Society Rapid publications
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Digital in-line holography with a spatially partially coherent beam
Get PDFWe propose in this paper an analytical solution to the problem of scalar diffraction of a partially coherent beam by an opaque disk. This analytical solution is applied in digital in-line holography of particles. We demonstrate that the reconstruction by means of fractional Fourier transformation is still possible when a spatially partially coherent beam is used. Numerical simulations and experiments have been carried out
A fast inversion method for highly conductive submicron wires on a substrate
Get PDFA numerical method is presented for sizing of highly conductive penetrable and perfectly electrically conducting (PEC) submicron wires on substrates. For efficiency, the Method of Auxiliary Sources is used in the forward model of the inverse Kirsch-Kress Method. The radius of the circular cross section of PEC and silver wires positioned on a semi-infinite silicon substrate is estimated based on numerically simulated scattered far field. The illumination is monochromatic, transverse electric (TE) polarised, and with fixed angle of incidence. Average relative errors smaller than 1% and 5% are achieved for PEC and penetrable wires, respectively, in the dynamic ranges 0.2–1.3 and 0.8–1.3 times the operating free-space wavelength, respectively. In all cases, the inversion time is less than 1 sec
Simulation and fabrication of active laser mirrors
Get PDFCommon laser mirrors made of copper for high power applications in metal working have to be cooled in order to minimize thermal deformations. This paper presents a new approach: The principal idea is to use metal-coated mirrors made of silicon carbide (SiC) and to preheat them. The mirror surface shall be manufactured so that the induced heat deforms it to the ideal form. Simulations concerning the thermal behavior prove the feasibility of the idea. The simulations are verified by interferometric measurement during heating
(lnP)5/(Ga0.47 In0.53 As)5 superlattice confined 1.5 µm multiquantum well laser grown by all- solid source atomic layer molecular beam epitaxy
Get PDFRoom temperature laser emission near 1.55µm is obtained in compressive strained multiquantum well separate confinement heterostructure grown at 340°C by all-solid source Atomic Layer Molecular Beam Epitaxy , where (lnP)5/(Ga0.47 In0.53 As)5, lattice-matched short period superlattices have been used as pseudoquaternary barrier to confine Ga0.27 In0.73 As wells . These preliminary results show that solid source Atomic Layer Molecular Beam Epitaxy is well adapted to fabricate advanced optoelectronic components including pseudoquaternary material
Synthetic modeling of astronomical closed loop adaptive optics
Get PDFWe present an analytical model of a single natural guide star astronomical adaptive optics system, in closed loop mode. The model is used to simulate the long exposure system point spread function, using the spatial frequency (or Fourier) approach, and complement an initial open loop model. Applications range from system design, science case analysis and AO data reduction. All the classical phase errors have been included: deformable mirror fitting error, wavefront sensor spatial aliasing, wavefront sensor noise, and the correlated anisoplanatic and servo-lag error. The model includes the deformable mirror spatial transfer function, and the actuator array geometry can be different from the wavefront sensor lenslet array geometry. We also include the dispersion between the sensing and the correction wavelengths. Illustrative examples are given at the end of the paper
Nanostructured surface fabricated by laser interference lithography to attenuate the reflectivity of microlens arrays
Get PDFA subwavelength-scale square lattice optical meta-material is fabricated using an interference photolithography process on the surface of a quartz microlens array. This nanostructuring of the quartz surface introduces an antireflective effect, reducing reflectivity between 10% and 30% and enhancing the transmissivity 3% in the visible spectrum. This approach permits fast fabrication on a 4-inch wafer covered with microlenses (non-flat surface) and produces monolithic devices which are robust to adverse environments such as temperature variations
Transmission of light in crystals with different homogeneity: using Shannon index in photonic media
Get PDFLight transmission in inhomogeneous photonic media is strongly influenced by the distribution of the diffractive elements in the medium. Here it is shown theoretically that, in a pillar photonic crystal structure, light transmission and homogeneity of the pillar distribution are correlated by a simple linear law once the grade of homogeneity of the photonic structure is measured by the Shannon index, widely employed in statistics, ecology and information entropy. The statistical analysis shows that the transmission of light in such media depends linearly from their homogeneity: the more is homogeneous the structure, the more is the light transmitted. With the found linear relationship it is possible to predict the transmission of light in random photonic structures. The result can be useful for the study of electron transport in solids, since the similarity with light in photonic media, but also for the engineering of scattering layers for the entrapping of light to be coupled with photovoltaic devices
Origins of ambiguity in the inversion of remote sensing reflectance signals by spectral matching in optically complex shelf seas.
Get PDFThe reported occurrence of multiple solutions in the inversion of remote sensing reflectance (Rrs) signals is of considerable significance for attempts to recover the concentrations of optically significant materials (OSMs) in shelf seas. The severity of this problem was assessed by quantifying the number of matches between individual multi wavelength remote sensing ‘observations’ and the entries in a pre-computed look-up table (LUT) spanning the range of possible observations. As a simplifying step, radiative transfer modeling was used to confirm the existence of a linear relationship between Rrs in the visible wavebands and the ratio of the backscattering to absorption coefficients (bb/a) over the full range of OSM concentrations likely to be found in shelf seas. This meant that an LUT of appropriate size and resolution could be constructed from bb/a vectors rather than Rrs spectra, with a considerable saving of computational effort. The number of matches in the LUT was then determined as a function of the degree of noise present in the observation and the strictness of the matching criterion (a simple least-squares fitting routine). Perfect matching for the six visible wavebands of the SeaWiFs satellite radiometer was achieved only when the ‘observed’ bb/a vector was represented exactly in the library. The introduction of noise representing observational errors rapidly led to multiple matches, as did relaxation of the matching criterion. As an example of the sensitivity of OSM recovery to errors of observation, it was found that an average error of 0.1%, statistically distributed across all wavebands, led to an average recovery error of 6.4% in CHL for 3000 randomly selected observations
General formulation of digital in-line holography from correlation with a chirplet function
Get PDFDigital in-line holography is revisited to propose a mathematical model that describes the recording-reconstruction process as a linear shift-invariant system with a pseudo-point spread function even when the images are out of the optimal plane in the sense of signal processing. A particular case is treated to show that the optimal plane is the best focus plane in the sense of optics. Next, an exact solution of the holographic reconstruction by correlation is given. By means of the previous results, we study the behavior of the result of the correlation function between the diffraction pattern function produced by an opaque disk and a chirplet function and between the diffraction pattern produced by a phase disk and the same chirplet function
3D-measurement with the stereo scanning electron microscope on sub-micrometer structures
Get PDFIn this paper the photometric or the so called "shape from shading" method is presented. In comparison to existing methods the efficiency of the detector system was considered and the requirements of the cosine Lambert's law for the angle distribution of the emitted electrons are suppressed. This new method was experimentally verified by measuring a steel sphere, a holographic grating and a hologram